Water level fluctuation patterns in the Colombo wetland area, insights into nature-based solutions for flood control

IntroductionUrban wetlands are considered an important nature-based solution to mitigate flood impacts in built-up areas like Colombo, Sri Lanka, due to rapid urbanization and intensifying rainfall events. Wetlands within the Colombo metropolitan region offer significant potential as nature-based solutions for flood mitigation; however, their hydrological functioning remains insufficiently quantified at high temporal resolution.MethodsThis study analyzes hourly water-level data from multiple locations over multiple years within the Colombo wetland system to investigate water-level dynamics, providing a comprehensive high-resolution analysis that remains limited in the existing literature. Data preprocessing included rigorous missing-value imputation using comparative statistical methods, with seasonal decomposition selected as the most consistent approach.Results and discussionTemporal variability was examined using correlation analysis, time-series and seasonal analyses, and continuous wavelet transform with Morlet wavelets, revealing a strong positive correlation between Kirimandala Street and Janakala Kendraya (r = 0.98) and a weak negative correlation between Diyasaru Park and Thalangama Lake (r = −0.14); time-series analysis indicated increasing trends at seven locations, no significant trends at Janakala Kendraya and Kaduwela, and a decreasing trend at Ewerihena; seasonal analysis showed a clear weekly periodicity across all locations. The wavelet results reveal dominant event-driven variability at longer time scales, reflecting cumulative rainfall effects, wetland storage, and delayed drainage processes, while short-period oscillations were comparatively weak and sporadic. Spatial heterogeneity in responses highlights the influence of wetland connectivity and surrounding urbanization on flood regulation capacity. The findings demonstrate that Colombo’s wetlands play a critical role in moderating flood dynamics and underscore the importance of conserving and integrating wetland systems into urban flood management strategies.